[sajacivil]

hello

i working on simulation a gravel bed open channel flow as rough bed but when i reach to determine wall B.C i do not know which value should i put for roughness height and roughness constant ,plz can any one help me

[vinerm]

Roughness height that Fluent expects is sand-grain roughness, i.e., if whole of the roughness was uniform. If you values for , then you can determine the roughness height to be entered in Fluent.

[sajacivil]

thank you sir ,but i'm working on non uniform gravel bed surface with different grains size in this case how can i determine the roughness height (i.e.what value should i used) and what do you mean of this "
If you values for Ra, then you can determine the roughness height to be entered in Fluent." i didn't understand sir can you explanation more,please


with regards

[vinerm]

You can use a roughness profile if roughness varies with position. However, the roughness measured using experiments or in the fields is not useful for modeling, not in it's original form. It needs to be converted into sand grain roughness. Quite possible that the new versions of Fluent accept measured roughness values as it is but you have to check that in manual.

[sajacivil]

sir i'm using version 16.1 is it has more difference from new versions and are you advice me to use last version for my case.

[vinerm]

Newer versions have roughness but only for icing simulation, applicable to nacelle icing primarily. So, the only option you have is to use sand grain roughness and that is available in both 16.1 and newer versions. However, newer versions allow roughness to be larger than the mesh size without resolving the roughness with fine mesh.